Patent GB-591490-A (GB)
Title: Electrical apparatus for measuring dimensions
IPC: G01B7/13
Filed: 1942-04-01
Abstract: 591,490. Electric dimension gauges. MALSALLEZ, P. April 1, 1942, No. 4360. Convention date, Jan. 24, 1941. [Class 40 (i)] [Also in Group XXXVI] Apparatus for measuring a dimension comprises a thermionic valve oscillator the frequency of which varies in response to variations in the capacitance, inductance, or resistance thereof caused by the dimension to be measured, and an oscillatory circuit having a fixed frequency including a thermionic detector valve, the fixed frequency circuit being inductively coupled with the variable frequency circuit and the variations in the anode current of the detector valve being used as a measurement of the dimensional variations of the object. An oscillatory circuit is formed by a fixed condenser c, Fig. 1, and inductance s, a condenser c1 the movement of the plates of which is controlled by the dimension to be measured, and a correcting or adjusting condenser c2. Oscillations. are maintained by a triode o which is inductively coupled by a transformer t to the grid of a detector valve d, the anode circuit of which includes a milliammeter m. The secondary t1 of the transformer t forms with a condenser k an oscillatory circuit of fixed frequency. As shown in Fig. 4, the condenser c1 comprises a set of fixed blades 2, secured to a metal case 1 by an insulating plate 3, and a set of movable blades 4 carried by a rod 5 which terminates in a head 8 of steel thermally insulated from the rod 5 by an ivory plate 9. The movable system is outwardly pressed by a spring 10 The case 1, which also carries the milliammeter m, is vertically adjustable by a rack and pinion 15, 16 on a column 12 carried by a base 13 and can be locked by a screw having a milled head 17. The base 13 encloses the oscillator and detector and is provided with an adjusting knob 21 for the correcting condenser c2 and a second knob (not shown) for adjusting the grid bias of the detector valve d by means of a potentiometer p, Fig. 1. On the base 13 is a support 18 formed with a V-groove for supporting a shaft 19 the diameter of which is to be measured. A standard shaft is placed in the support 18 and the case 1 is lowered until the movable system 4 is in its mean position as indicated by a reference mark on the rod 5. The case 1 is then locked in position and the condenser c2 and potentiometer p are adjusted until the milliammeter m is brought to zero. The standard shaft is then replaced by the shaft to be measured, and the difference in diameter is indicated by the milliammeter, which may be graduated in terms of length. The column 12 may be provided with a scale 12a enabling a standard shaft to be dispensed with. Fig. 8 shows a modification for measuring the internal diameter of a cylinder 23. The case 1b containing the condenser c1 is part spherical and is provided with two fixed abutments 25 at 120 degrees from the movable head 8. Fig. 9 shows another modification for verifying the dimensions of gauges. The gauge 28 is formed by a metal ring formed with a slot having a step 29 so that maximum and minimum dimensions h2, h1 are defined. The movable plate of the condenser c1 is formed by a metal plate 30 mounted on the end of an insulating handle 31, the fixed plate being formed by the edges of the slot in the ring 28. The dimension to be measured may vary an inductance instead of a capacitance. The inductance and capacitance of the oscillatory circuit may be fixed, the dimension to be measured varying a resistance in the oscillatory circuit. The Specification as open to inspection under Sect. 91 describes also the modification shown in Fig. 12 (Cancelled). An oscillating circuit is formed by a condenser 40 and inductance 41, with a condenser 42 for adjusting the zero and the measuring condenser 43. This circuit is connected to the grid of an oscillating valve 44, which is connected to a coupling and amplifying 'valve 45 coupled through a transformer 47 to a mean frequency amplifier 46. This is coupled through a transformer 48 to a rectifier 49, in the output circuit of which is a measuring instrument 50 and a recorder 51. A measuring instrument 53 enables the resonance curve to be defined and the modification thereof at the moment of measuring to be determined. This subject-matter does not appear in the Specification as accepted.